In optics, a beam of light is said to be coherent if its phase (the phase of the oscillating electric and magnetic fields) varies smoothly along the beam rather than going through discontinuous changes. More precisely, the beam has a "coherence length" which is the average length over which the phase oscillates smoothly. For light from an ordinary lightbulb, this is only about one wavelength, because the light is made up of photons which are not in phase with each other. For a laser beam, the photons are in phase with each other, and the coherence length is about 50cm. Coherent light will produce interference patterns when passed through a diffraction grating.

Mark Williams' Coherent Operating System was a UNIX-like OS that ran on early PC's (Original 8086-80286 I think) and then later was ported to the 80386 with its protected mode architecture.

Unfortunately it wasn't all THAT UNIX-like, and so if you were used to working in "real" UNIX you would likely have been somewhat dissappointed.

That having been said they did a great job with the minimal resources they had at their disposal, and their support engineers were always very helpful when we called.

Co*her"ent (?), a. [L. cohaerens, p. pr. See Cohere.]


Sticking together; cleaving; as the parts of bodies; solid or fluid.



Composed of mutually dependent parts; making a logical whole; consistent; as, a coherent plan, argument, or discourse.


Logically consistent; -- applied to persons; as, a coherent thinker.



Suitable or suited; adapted; accordant.


Instruct my daughter how she shall persever, That time and place, with this deceit so lawful, May prove coherent. Shak.


© Webster 1913.

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